Equisetaceae are the sole survivors of a line of plants going back three hundred million years; members of this family gave rise to many of our coal deposits.  Equisetaceae are circumboreal and are widespread through the United States.  In the semi-deserts, foothills, and mountains of the Four Corners they are common near streams and in wet forests and meadows.

     The various Equisetum are commonly called "Horsetails" or "Scouring Rush".

Equisetum laevigatum (Smooth Scouring Rush)
Equisetaceae (Horsetail Family)

Foothills, montane. Streamsides, wetlands. Summer.
Above and left: Near Canyons of the Ancients National Monument, August 30, 2014.

Stems of Equisetum laevigatum are annual (although some may over-winter), they grow 20-150 centimeters tall and 2-8 millimeters thick, and they are all the same; i.e., there are not separate sterile and fertile stems.

Several additional characteristics distinguish this species: stems have 10-32 longitudinal ridges which are usually smooth feeling but under high magnification can sometimes be seen to have transverse wrinkles; the sheath at each node is mainly green with one dark band; the teeth of the sheath are black with a white margin and are often early deciduous; and the cones (10-25 mm long) are usually blunt-tipped.

The photograph above shows a typical massing of Equisetum laevigatum. As you can see, most stems do not branch, but some, as shown at left, do branch several times.

Linnaeus named this genus in 1753 from specimens collected in Europe. Alexander Braun named and described this species in 1844 from specimens collected, probably in 1838, in St. Louis, Missouri by naturalist, plant collector, and nurseryman, Nicholas Riehl. (Riehl collected widely in St. Louis and sold his collection to Henry Shaw, who, with George Engelmann, started Shaw's Garden, what is now the Missouri Botanical Garden. Riehl also sold Shaw the first trees planted in Shaw's Garden.)

"Equisetum", is derived from the Latin "equus" for "horse" and "seta" for "bristle".  "Laevigatum" is Latin for "smooth".

Foothills, montane. Streamsides, wetlands. Summer.
Near Canyons of the Ancients National Monument, August 30, 2014.

The lower right photograph of the three at left shows the entire bulge of the sheath, topped by black teeth with their tips fallen away. A close look at various stems shows many different patterns and textures, especially at the top of each sheath.

Equisetum laevigatum (Smooth Scouring Rush)
Equisetaceae (Horsetail Family)

Foothills, montane. Streamsides, wetlands. Summer.
Near Canyons of the Ancients National Monument, June 1, 2015 and August 30, 2014.

Cones have numerous scales with sporangia on the lower surface. By late August most sporangia have spilled their spores and then cones are ready to fall from the stems.

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Range map for Equisetum laevigatum